Digital image sensors, such as CMOS or CCD sensors, include a plurality of photosensors each configured to convert photons incident upon the photosensors (“captured light”) into electric charge. The electric charge can then be converted into image data representing the light captured by each photosensor. The image data includes a digital representation of the captured light, and may be manipulated or processed to produce a digital image capable of display on a viewing device. Image sensors are implemented in integrated circuits (“ICs”) with a physical surface that may be divided into a plurality of pixel regions (for instance, one or more photosensors and attendant control circuitry) configured to convert light into an electrical signal (charge, voltage, current, etc.). For convenience, pixel regions within an image sensor may also be referred to as image pixels (“IPs”) and the aggregate of the pixel regions or image pixels will be referred to as the image sensor region. An image sensor IC typically will also include areas outside of the image sensor region, for example certain types of control or interface circuitry.
Image sensors include a variety of control lines, reset lines, and output lines (collectively “input/output” or “I/O” lines herein) to transmit control signals, reset signals, and image data to and from the pixels of the image sensor. As photosensors for most applications perform better with an unobstructed path for light incident upon the photosensors, the portions of the surface area of an image sensor dedicated to couple I/O lines to the pixels reduce the amount of image sensor surface area that can contain photosensors with unobstructed light paths. The proportion of image sensor surface area containing unobstructed photosensors is referred to herein as the “fill factor” of the image pixels.